Electrolytes:- Part 2 – Sodium (Na+), Blood and Serum

Sodium (Na⁺)

Sample for Sodium (Na⁺)

1. This test is done on the serum of the patient.
   1. A random sample can be taken.
2. Heparinized plasma and whole blood without sodium heparin may be used.
3. Twenty-four hours urine sample may be collected without the addition of preservatives.
   1. Can store the serum or urine at 2° C to 4 °C.
4. Other samples can be:
   1. Feces.
   2. Sweat.
   3. Gastrointestinal fluids.

Precautions for the estimation of Sodium (Na⁺)

1. Avoid hemolysis (Although it does not cause much difference in serum or plasma sodium values).
2. Lipemic serum needs to be ultracentrifuged unless the direct-selective electrodes measure sodium.

Indications for Sodium (Na⁺)

1. This is the routine workup of the patient.
2. This is done to evaluate electrolytes and acid-base balance.
3. To evaluate water intoxication, water balance, and dehydration.
4. It is estimated to diagnose and treatment of dehydration and overhydration.

Pathophysiology of Sodium (Na⁺)

1. Sodium is the major cation of the extracellular fluid. It has a major influence on plasma osmolality.
   1. It is adjusted by the anti-diuretic hormone (ADH) and thirst receptors to maintain the plasma volume and osmolality.
   2. Aldosterone causes tubular reabsorption of sodium.
   3. Changes in the serum sodium reflect changes in water balance rather than sodium balance.
2. Sodium is a very important cation from a quantitative standpoint and because of its influence on electric neutrality.
3. The average adult body contains 80 grams of sodium.
   1. 35 grams is present in the extracellular fluid.
   2. Daily, the average person takes 3 grams of sodium in salt forms like chloride, sulfate, or other salts.
      1. Also, excrete the same amount of 3 grams per day.
      2. Dietary need of sodium = 90 to 250 meq//day.
   3. The normal daily diet contains NaCl 8 to 15 grams which are completely absorbed in the gastrointestinal tract.
      

      Sodium and Potassium distribution

4. Sodium is the most common cation of the blood by almost 90%.

Sodium and the role of kidneys:

1. 100% of sodium is filtered through the glomerulus.
2. 70 to 80% is reabsorbed in proximal tubules ^(water and chloride).
3. 20 to 25% is reabsorbed in the loop of Henle (with water and chloride).
4. Kidneys are the main regulator of sodium in the body, which excretes the excess.
   

   Sodium absorption and role of kidneys

5. Distribution of the sodium (Na⁺):
   1. The sodium level is the reverse of Potassium that sodium is 140 meq/L extracellular and 5 meq/L intracellular.
      

      Sodium distribution in intracellular and extracellular space

Functions of the sodium (Na⁺):

1. Sodium is a major component of extracellular osmolality. It is almost half the osmolality of the plasma.
   1. So Sodium’s main function is to maintain osmotic pressure and acid-base balance.
2. Sodium also helps to transmit nerve impulses.
   1. Sodium work with potassium and calcium to maintain the neuromuscular irritability for the conduction of nerve impulses.
   2. Neuromuscular, Sodium helps in the acid-base balance through sodium bicarbonate and sodium phosphate.
   3. Sodium takes part in cellular chemical reactions and membrane transport.
3. The body can maintain the sodium level very well except for a few pathological conditions.
4. Maintenance of sodium level depends upon:
   1. Renal blood flow.
   2. Carbonic anhydrase activity.
   3. Aldosterone.
   4. Other steroids hormones control through:
      1. Anterior pituitary gland.
      2. Renin enzyme secretion.
      3. Antidiuretic hormone ( ADH ).
      4. Vasopressin secretion.
5. Sodium is a result of a balance between dietary intake and renal excretion.
6. Aldosterone acts by:
   1. Stimulating the Kidney to conserve sodium.
   2. And Decrease renal loss.
7. ADH controls:
   1. Reabsorption of water at distal tubules.
   2. .This will affect by the concentration or dilution of sodium.
8. Physiologically Sodium and water are interlinked.
   1. Increased free body water = Sodium diluted, Na concentration decreases, Kidney conserves sodium and excrete water.
   2. Decreased free water = Serum sodium will rise, now the Kidney will conserve water. Na⁺ level became normal.

Active transport of sodium (Na⁺):

1. This is found in most of the cells, especially muscles and nerves.
2. The excitable tissue has a high Na⁺, K⁺, and ATPase concentration.
3. With the help of the ATPase enzyme in the cell membrane, three molecules of Na⁺ go out while only two molecules of K⁺ go in.
4. So inside is negatively charged.
   

   Sodium and Potassium active transport

   

   Sodium transport is an active process

Hyponatremia level and Signs/Symtoms :

1. When the level is < 125 meq/L (<135 mmol/L).
   1. < 120 meq/L is severe hyponatremia.
   2. The patient will feel weak.
2. When Level < 115 meq/L.
   1. The patient will have confusion and lethargy.
   2. May progress to stupor and coma.
3. There is a decreased glomerular filtrate rate, as seen in congestive heart failure.
   1. This is seen in the case of:
      1. low salt intake.
      2. There is premenstrual retention of sodium and water.
      3. Adrenocortical hyperfunction.
      4. Hyperaldosteronism.

Hypernatremia level and Signs/Symtoms:

1. >160 meq/L is the critical value for the patients.
   1. The patient will have dry mucous membranes.
   2. Thirst.
   3. Agitation and restlessness.
   4. Hyperreflexia.
   5. Mania and convulsion.
2. There is increased excretion of sodium in the urine.
3. It is seen in:
   1. Hypoaldosteronism.
   2. Adrenal failure.
   3. Diuretic therapy.
   4. Salt losing nephritis.
   5. Physiologically increased intake of salt.

NORMAL Sodium (Na⁺)

Source 1

Age	meq/L
Premature cord blood	116 to 140
Premature 48 hours	128 to 148
Newborn cord blood	126 to 166
Full-term	133 to 146
Infants	139 to 146
Child	138 to 145
Adult	136 to 145
>90 years	132 to 146
Urine 24 hours	meq/day
	Male	Female
6 to 10 years	41 to 115	20 to 69
10 to 14 years	63 to 177	48 to 168
Adult	40 to 220
Sweat	meq/L
Child and adult	10 to 40
Cystic fibrosis	70 to 190
Feces	<10 (7.8 ± 2)
Saliva	meq/L
Without stimulation	6.5  to 21.7
After stimulation	43 to 46
CSF	136 to 150
Amniotic fluid	meq/L
28 weeks	124 to `48
48 weeks	115 to 139

• To convert into SI units x 1.0 = mmol/L

Source 2

• Sodium = 136 to 145 meq /L
• Infants = 133 to 142 meq /L.
  • Premature infants = 132 to 140 meq/L.
• Urine        = 40 to 220 meq/day with an average sodium intake of around 8 to 15 grams per day.
  • (varies with dietary intake).
• CSF = 136 to 150 meq/L.
• Feces = mean value is <10 meq/day.

Causes of Hypernatremia (Increased serum sodium):

1. Dehydration.
2. Insufficient water intake.
3. Primary aldosteronism.
4. Cushing’s syndrome.
5. Diabetes insipidus.
6. Coma.
7. Excessive sodium in intravenous therapy.
8. Excessive sweating.
9. Vomiting.
10. Extensive thermal burns.
11. Loss from GI tract.

Hyponatremia (Decreased serum sodium):

1. Deficient dietary intake.
2. Decreased sodium in the I/V therapy.
3. Diuretics.
4. Chronic renal insufficiency.
5. Aspiration of pleural or peritoneal fluids.
6. Excessive water intake.
7. Congestive heart failure.
8. Ascites.
9. Pleural effusion.
10. Ectopic secretion of ADH.
11. Pyloric obstruction.
12. Malabsorption syndrome.
13. Diabetic acidosis.
14. Hypothyroidism.
15. Nephrotic syndrome.
16. Absolute loss of sodium from the body:
    1. Prolonged vomiting.
    2. Excessive sweating.
    3. Prolonged diarrhea.

Hyponatremia, when the patient is hypovolemic, may be seen in:

1. Renal losses due to:
   1. Diuretics
   2. medullary renal disease
   3. Addison’s disease
2. External losses  due to:
   1. Gastrointestinal losses

Pseudohyponatremia may be seen in:

1. This condition is usually caused by an excess of lipids in the serum. Serum sodium ions are not dissolved in the lipids.
   1. Hyperglycemia
   2. Hyperlipidemia
   3. Hyperproteinemia

Sodium (Na⁺)  level in blood and urine in various conditions:

Various clinical conditions	Sodium (Na+) level in the blood	Sodium (Na+) level in urine
Diarrhea	Decreased	Decreased
Dehydration	Increased	Increased
Malabsorption	Decreased	Decreased
Starvation	Normal	Normal or Increased
Excessive sweating	Decreased	Decreased
Pyloric obstruction	Decreased	Decreased
Congestive heart failure	Normal or decreased	Decreased
Pulmonary emphysema	Normal	Decreased
Acute renal failure	Decreased	Decreased
Chronic renal failure	Decreased	Increased
Renal tubular acidosis	Decreased	Increased
Primary aldosteronismm	Increased	Decreased
Adrenal cortical insufficiency	Decreased	Increased
Diabetic acidosis	Decreased	Increased
Diabetes inspidus	Normal or increased	Normal
Thiazide diuretics	Decreased	Increased
Mercurial diuretics	Decreased	Increased
Diamox (Acetazolamide)	Decreased	Increased

Critical value when the patient needs an immediate intervention:

1. Na⁺ < 120 meq/L. The patient will have weaknesses and neurologic symptoms.
2. Na⁺ > 160 meq/L. This may cause heart failure.

• Too rapid correction of hyponatremia can lead to central pontine myelin-lysis.
• The too-slow correction will lead to cerebral edema.

 Note: Please see more details on Serum electrolytes.

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